摘要
马哈螺(Maikhanellids)是一类具单壳的、壳体表面发育特殊鳞片状纹饰的软体动物化石。目前对maikhanellids鳞片状纹饰的研究主要涉及整体形态和分类,关于鳞片状纹饰的组成和内部结构的研究为数甚少。马哈螺科中Mediata属以壳顶大(约占整个壳面的1/3–1/2)、不同大小的长卵形鳞片状纹饰、背部具有一条从壳体前端延伸至壳体后端的宽脊、无规则的生长纹等特征有别于该科其他各属。本文基于陕南寒武系幸运阶宽川铺组产出的大量保存精美的Mediata标本,详细描述了Mediata鳞片状纹饰的形态特征、超微结构和原始矿物组成。Mediata的纹饰鳞片从外到内可分为外、中、内三层。外层为覆盖整个鳞片状纹饰的原始角质层。中层由磷灰石集聚体组成,该集聚体在中层外部表现为紧密且无定形排列,说明其原始成分可能为有机质;而在中层内部集聚体则排列成纤维状结构,暗示其原始矿物成分可能为文石。内层由平行于鳞片长轴方向的束状结构组成,束状结构内部有许多相互平行的微米级细长空心棱柱状结构,棱柱状结构之间被有机膜分隔。Mediata内层的超微结构和蒙古西南部纽芬兰统Bayangol组发现的软体动物Postacanthella voronini的柱状有机基质在形态和大小上非常相似,因此笔者推测Mediata内层束状结构很可能是一种有机框架,代表了目前已知最早的有机框架的化石记录。如果这种有机框架是用来控制鳞片状纹饰分泌方解石,这表明在寒武纪幸运期该属可能就具有了同时分泌方解石和文石两种矿物以构筑坚硬壳体的能力,那么这种壳体结构就为解释寒武纪早期软体动物类群的兴盛提供了新的依据。
Maikhanellids is a mollusk fossil with a single shell which is ornamented with a large number of scales.At present,the research on maikhanellids scaly ornaments mainly involves the overall morphology and classification,and there are few studies on the composition and internal structure of the scaly ornaments.The genus Mediata in Maikhanellidae is distinguished from other genera in the family by its large shell apex(about 1/3–1/2 of the entire shell surface),long ovate scales,a wide ridge on the back extending from the front of the shell to the posterior end of the shell,and irregular growth lines.Here we described the morphological characteristics,internal ultrastructure and primitive mineral composition of Mediata shell scales based on a large number of secondarily phosphatized fossil Mediata from the Kuanchuanpu formation in the southern Shaanxi.The shell scales of Mediata are subdivisible into outer,middle and inner layers.The outer layer covering the whole shell ornaments scales represents the primitive periostracum.The middle layer is composed of subspherical apatite aggregates.As seen from the outside,the apatite aggregates appear to be amorphous and closely arranged,suggesting that the original composition is organic.From the inside of scales,the apatite aggregates are observed to be arranged in fibrous layers,suggesting that the original mineral is aragonite.The inner layer,originally occupying the hollow space of the scales,consists of a bundle-like structure parallel to the long axis of the scale.Inside the bundle structure there are many elongated hollow prismatic structures in the micron scale parallel to each other.Inside the bundle are many micron-level,elongated hollow prismatic structures parallel to each other.The prismatic structures are separated by organic membranes.The ultrastructure of the inner layer of Mediata scales is quite similar with the prismatic organic membrane of the Postacanthella voronini,a mollusc from the Cambrian Terreneuvian Bayangol formation at Bayan Gol in the Zavkhan B
作者
岳宁
宋祖晨
王邓
何凯悦
雍媛媛
郝文静
鱼驰洋
孙洁
郭俊锋
田莹
韩健
YUE Ning;SONG Zuchen;WANG Deng;HE Kaiyue;YONG Yuanyuan;HAO Wenjing;YU Chiyang;SUN Jie;GUO Junfeng;TIAN Ying;HAN Jian(Shaanxi Key Laboratory of Early Life and Environments and State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi’an 710069,P.R.China;School of Earth Science and Resources,Key Laboratory of Western China’s Mineral Resources and Geological Engineering,Ministry of Education,Chang’an University,Xi’an 710054,P.R.China;Key Laboratory of Mariculture&Stock Enhancement in North China’s Sea,Ministry of Agriculture and Rural Affairs,Dalian Ocean University,Dalian 116023,P.R.China)
出处
《微体古生物学报》
CSCD
北大核心
2023年第1期1-12,共12页
Acta Micropalaeontologica Sinica
基金
中国科学院战略性先导科技专项(B类)资助项目(XDB26000000)
国家自然科学基金项目(41672009,41621003,41772010,41720104002,42172016)资助。
关键词
马哈螺
鳞片状纹饰
有机框架
软体动物
方解石
文石
寒武纪早期
maikhanellids
scaly ornaments
organic matrix framework
Mollusk
calcite
aragonite
Early Cambrian
